Currently, drywall is almost universally used for interior walls in houses and buildings. The drywall comes in large sheets which are fitted together to make a solid wall surface having an appearance approximating the appearance of a plastered wall. The cracks between the sheets must be covered by a tape and mastic which is thereafter sanded to give the plastered wall appearance.
This means that, in the interior corners of the walls, it is necessary to fit the tape and mastic properly and almost perfectly along the 90.degree. angle between the two walls that meet in the corner. The corner finisher tool should have enough freedom of movement to enable it to position and accommodate itself to irregularities on the wall surface. The tape should not either span the corner or fit into a crack between the wallboards. The mastic should be applied as smoothly as possible because it is difficult to sand off the excess mastic in the corner. An example of a prior art corner finisher tool is found in U.S. Pat. No. 4,767,297.
Among other things, there are many different kinds of tools which may be used for applying the tape and mastic to both the flat seams on a wall surface between drywall sheets and the corners where drywall sheets abut. Three coats of mastic are applied in different thicknesses over the tape. Therefore, there are many tools which are generally parts of a mastic application system and which should be changed quickly and easily as the workman encounters different needs during his work.
Therefore, it is a common practice to provide a quick disconnect coupler for joining the various drywall mastic applicator tools to each other. However, heretofore there have been problems because there were frequent failures of the locking mechanism on the coupler, such as for securing a corner finisher tool to other equipment for supplying a mastic. In particular, it was difficult to secure a corner finishing tool to a mastic source because the finisher tended to be larger and heavier than other tools, because the need for precision in the corners is much more severe than the need for precision on a strictly flat wall surface, and because the pressure of mastic being squeezed out of a pressurized delivery system tends to push the finisher off the tool for delivering the mastic.
The prior art used a U-shaped spring, into which a tool snapped, in order to solve the simultaneous problems of providing quick disconnect and secure locking after the connection was made. The troubles were multiplied because the corner finisher tool could easily separate from the associated tools and fall to the ground. The corner finisher tool then might be damaged. While the tool itself could be replaced, if the tool fell in a bathroom, for example, the ceramic tile, a bath tub, or another fixture could be chipped or otherwise severely damaged by the falling tool. These problems are often difficult and expensive to repair.